Chin ptosis years after a chin implant. What procedure do I need? (photos)

Ptosis means hanging down. The implant is not hanging down, rather the lateral ends or "wings" of the implant are being pulled up when you smile.
There are possible reasons for this:
the implant is not seeded correctly. The implant has a lip that wraps over the margin of the mandible. It is possible that the "lip" did not wrap around the border of the mandible or got dislodged thus when the facial muscles pull, they move the implant wingsThe implant was not placed under the periosteum, so muscle attaches to the implant capsule and the implant moves when you smile.
The solution will be to create a new subperiosteal pocket for the implant and seed it properly on the lower mandibular border.
Hope this helps!

While the specifics of your chin implant are unknown (size, position on bone), you appear to be correct about the dynamic ptosis particularly if it existed before the chin implant. Normally the volume added by the implant improves or corrects dynamic ptosis. More horizontal chin augmentation still may and there is room for further projection. With your chin augmentation rest and good chin shape at rest I would be careful about doing anything as there is a delicate balance between improving one problem but causing another.